Richard Diamond, Private Detective: Death and the Letter (1950 radio adventure) 

Original Airdate: Nov. 8, 1950.
Cast: Barton Yarborough (Chief, thug #1), Virginia Gregg (Nancy Lang), Lou Krugman (Guillardo), and Barney Phillips (thug #2, Skipper).
A dying man hands Diamond a white envelope and starts the former cop on a case involving international intrigue, a beautiful woman, and murder.
Dick Powell stars as Rick Diamond, a one-time WWII OSS agent who then becomes an NYC cop in the Fifth Precinct. Later he decides to strike off as a private gum-shoe on his own with offices at 55th and Broadway and proceeds to take cases of adventure and intrigue and often cases proceed to take him.